1. Field of the Invention
The present invention relates generally to a barrel shifter, and more specifically a barrel shifter which shifts input data at high response speeds.
2. Description of the Prior Art
Where a barrel shifter is made up of a number of selectors composed of a plurality of N- or P-channel MOS transistors, since there inevitably exists a threshold voltage (on-voltage of the MOS transistor), it is impossible to obtain a sufficiently high ("1") level or low ("0") level shifted output data at the output terminal of the barrel shifter. In addition, since a drain voltage of the MOS transistor reaches a voltage level (V.sub.DD -V.sub.TH, where V.sub.DD denotes a supply voltage and V.sub.TH denotes a threshold voltage) in accordance with a time constant curve, there exists another problem in that a rise time or a fall time of the MOS transistor is relatively long, thus resulting in a low response speed or a low input data shifting speed.
To overcome the above-mentioned drawbacks, it is possible to configure the barrel shifter by means of CMOS transistors in which an NMOS transistor is connected in parallel with a PMOS transistor in complementary fashion. In this case, although a sufficiently high ("1") or low ("0") output signal can be obtained, there still exists the other problem such that the number of MOS transistors is doubled and therefore the barrel shifter becomes bulky in circuit configuration.
The arrangement and the operation of the prior art barrel shifter will be described hereinafter in greater detail with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT.